J. Geophys. The geomagnetic activity levels of the Earth are measured by the fluctuation of the Earth's magnetic field in, This page was last edited on 15 June 2023, at 22:26. Solar-Terrestrial Phys. Space Phys. At high F10.7, when the ionosphere F layer is relatively strong, observed plasmasphere refilling rates at geosynchronous altitudes are relatively weak (Lawrence et al., 1999; Gallagher et al., 2021). (2015) presented such TEC data and showed that, when driven from below by assimilated data, a computer simulation of the thermosphere reproduces about 50% of the observed variability. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. doi:10.1029/2008JA013433, Lhr, H., Liu, H., Park, J., and Mller, S. (2011). The Ionospheric Connection Explorer Mission: Mission Goals and Design. Space Phys. The effects of SAPS on the thermosphere and ionosphere are global SAPS drive large zonal winds in the subauroral region SAPS cause changes in neutral temperature, composition and electron density 1. doi:10.1002/2017SW001780, Krall, J., Huba, J. D., Denton, R. E., Crowley, G., and Wu, T.-W. (2014). (the neutral atmosphere).[17][18]. 36, 14. Vertical coupling in the atmosphere-ionosphere system, from the troposphere to the thermosphere-ionosphere. (2021). doi:10.1029/2020JA028727, Gallagher, D. L., and Comfort, R. H. (2016). Res. There are multiple causes of sporadic-E that are still being pursued by researchers. MSIS-86 Thermospheric Model. As shown graphically in Figure 1D, and described by Richards and Torr (1985), the limiting H+ outflow flux is proportional to the supply of O+ ions and H atoms at outflow source height Z0 (7001,100km): where Tn is the thermosphere temperature, HO+ is the O+ scale height, and the leading coefficient has been updated from 2.50 to 2.85 based on a corresponding update to the H-O+ charge exchange reaction rate. doi:10.1029/93GL03391, Singh, N., and Horwitz, J. L. (1992). Space Phys. 126, e2020JA028947. Sami3/SD-WACCM-X Simulations of Ionospheric Variability during Northern winter 2009. 41, 82088214. Plasma in the Geomagnetic Tail. J. Geophys. doi:10.1002/2014JA019982, Park, C. G. (1970). Solar particle event Polar cap absorption events, Super Dual Auroral Radar Network (SuperDARN), High Frequency Active Auroral Research Program, TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics), "General theory of terrestrial magnetism", "Carl Friedrich Gauss General Theory of Terrestrial Magnetism a revised translation of the German text", Fessenden and Marconi: Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century, "On the elevation of the electrically conducting strata of the earth's atmosphere", worldradiohistory.com: Broadcast listening in the pioneer days of radio on the short waves, 1923 1945 Jerome S. Berg, "Firsts in the Space Race. Equatorial spread F disturbances during sunrise hours is observed, . The more magnetically active the Sun is, the more sunspot active regions there are on the Sun at any one time. The most realistic model, TIMEGCM, gives the best results; MSIS/HWM07 also works well. Authors. Modeling the Plasmasphere with Sami3. While older simulations (Fang et al., 2013) support the finding that tidal forcing accounts for about one half of observed variability, recent work (Zawdie et al., 2020) comes closer to determining the state of the ionosphere-thermosphere system in enough detail to now-cast the upper-atmospheric source of refilling outflows. Earth Space Sci. However, during intense sporadic E events, the Es layer can reflect frequencies up to 50MHz and higher. The message received was three dits, the Morse code for the letter S. To reach Newfoundland the signal would have to bounce off the ionosphere twice. Additional ionization can also occur from direct heating/ionization as a result of huge motions of charge in lightning strikes. J. Geophys. As the frequency increases, each wave is refracted less by the ionization in the layer, and so each penetrates further before it is reflected. 123, 51195139. In this study we recorded conditions at outflow source height Z0, values computed using Eq. 4 Discussion: Can These Effects Be Forecasted? The Ionosphere. However, we are not yet able to forecast these outflows. doi:10.1016/j.jastp.2006.05.030, Cai, X., Burns, A. G., Wang, W., Qian, L., Solomon, S. C., Eastes, R. W., et al. Space Phys. Space Weather Space Clim. Review of Radiation belt Relativistic Electron Losses. doi:10.1002/2015JA022126, Krall, J., and Huba, J. D. (2019b). Day-to-day Variability in the Thermosphere and its Impact on Plasmasphere Refilling. J. Geophys. Total refraction can occur when the collision frequency of the ionosphere is less than the radio frequency, and if the electron density in the ionosphere is great enough. Ultraviolet (UV), X-ray and shorter wavelengths of solar radiation are ionizing, since photons at these frequencies contain sufficient energy to dislodge an electron from a neutral gas atom or molecule upon absorption. Regions of the ionosphere, showing the D, E, and F layers. Space Phys. - Quora. [27] Planets known to have ionospheres include Venus, Mars,[28] Jupiter, Saturn, Uranus, Neptune and Pluto. The F layer or region, also known as the AppletonBarnett layer, extends from about 150km (93mi) to more than 500km (310mi) above the surface of Earth. Space Phys. Earth's atmosphere contains a series of regions that have a relatively large number of electrically charged atoms and molecules. 69, 378386. Ionization here is due to Lyman series-alpha hydrogen radiation at a wavelength of 121.6 nanometre (nm) ionizing nitric oxide (NO). Res. Space Phys. Res. At heights of above 80km (50mi), in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. [10], In 1926, Scottish physicist Robert Watson-Watt introduced the term ionosphere in a letter published only in 1969 in Nature:[11]. J. Geophys. Control of Equatorial Ionospheric Morphology by Atmospheric Tides. T. J. Fuller-Rowell, M. V. Codrescu, R. G. Roble, A. D. Richmond The SuperDARN radar project researches the high- and mid-latitudes using coherent backscatter of radio waves in the 8 to 20MHz range. Around the same time, Robert Watson-Watt, working at the Radio Research Station in Slough, UK, suggested that the ionospheric sporadic E layer (Es) appeared to be enhanced as a result of lightning but that more work was needed. 9, A39. Temperatures in the upper thermosphere can range from about 500 C (932 F) to 2,000 C (3,632 F) or higher. Res. (1966). Editor J. Frihagen (New York: North-Holland), 387. High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. The critical frequency is the limiting frequency at or below which a radio wave is reflected by an ionospheric layer at vertical incidence. Some of the radio-frequency energy is given up to this resonant oscillation. [25] The Galileo navigation system uses the NeQuick model.[26]. As it stands, measured post-storm plasmasphere refilling rates at any given height vary by as much as an order of magnitude (Denton et al., 2012), Figure 1. The research of JH was also supported by NSF grant AGS 1931415. 105, 2303523053. 71, 14211426. A. Ratcliffe researched the topic of radio propagation of very long radio waves in the ionosphere. 90, 52615268. discovered quasiperiodic southward-moving MSTIDs during nighttime, likely caused by gravity waves in the thermosphere. Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10MHz and may contribute a bit to absorption on frequencies above. Geophys. 8:712616. doi: 10.3389/fspas.2021.712616. chorus. In addition, solar flares can generate hard X-rays (wavelength < 1 nm) that ionize N2 and O2. doi:10.1029/2018JA025323, Denton, R. E., Wang, Y., Webb, P. A., Tengdin, P. M., Goldstein, J., Redfern, J. The ionosphere is a very active part of the atmosphere, and it grows and shrinks depending on the energy it absorbs from the Sun. Good agreement between SAMI2 and Eq. Seasonal, Diurnal, and Solar Cyclical Variations of the Limiting H Flux in the Earths Topside Ionosphere. (2008). When a radio wave reaches the ionosphere, the electric field in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Coordinates for Mapping the Distribution of Magnetically Trapped Particles. Thermospheric Composition O/N Response to an Altered Meridional Mean Circulation during Sudden Stratospheric Warmings Observed by GOLD. TIE-GCM is a coupled thermosphere-ionosphere model that uses a finite difference scheme to solve the nonlinear equations of conservation of mass, energy, and momentum for neutral and ion species . Res. The thermosphere is typically about 200 C (360 F) hotter in the daytime than at night, and roughly 500 C (900 F) hotter when the Sun is very active than at other times. Within approximately 20 degrees of the magnetic equator, is the equatorial anomaly. How Does the Thermosphere and Ionosphere React to a Geomagnetic Storm? Typically, as in the SAMI2 runs above, we compute densities using MSIS (Hedin, 1987; Picone et al., 2002) and compute winds using the Horizontal Wind Model (Hedin, 1991; Drob et al., 2008; Drob et al., 2015). Radio propagation depends uniquely on electron density. An ionospheric model is a mathematical description of the ionosphere as a function of location, altitude, day of year, phase of the sunspot cycle and geomagnetic activity. The ionosphere and thermosphere (IT) is coupled in an intricate way to the magnetosphere via electromagnetic fields, energetic charged particles, currents and neutral gas, and across many spatial and temporal scales. Space Phys. This propagation occurs every day during June and July in northern hemisphere mid-latitudes when high signal levels are often reached. doi:10.1029/2008JA013060, Qian, L., Burns, A. G., Solomon, S. S., Smith, A. K., McInerney, J. M., Hunt, L. A., et al. The Dual Role of ELF/VLF Chorus Waves in the Acceleration and Precipitation of Radiation belt Electrons. Res. Time-dependent Response of the Terrestrial Exosphere to a Geomagnetic Storm. Note that the much lower value of nH at F10.7=210 accounts for the counter-intuitive result that outflow fluxes are smaller at solar maximum, when the ionosphere is strongest. J. Geophys. Contradictions on CO2 concentration trends in the MLT region have been solved; in . https://doi.org/10.3389/fspas.2021.712616. At higher altitudes, in the magnetosphere and in the solar wind, matter is almost completely in plasma state, and dominated by electromagnetic forces. 125, e2020JA028331. Space Phys. Dashed lines in each plot indicate observed refilling rates. HAARP was started in 1993 as a proposed twenty-year experiment, and is currently active near Gakona, Alaska. 119, 44004411. During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F1 layer. Global Modeling of Equatorial Spread F with Sami3/WACCM-X. During this time very low frequency (330kHz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it. The Naval Research Laboratory (NRL) Sami2 is Another Model of the Ionosphere (SAMI2) and Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere codes have shown that thermosphere composition and winds significantly affect H+ outflows from the topside ionosphere. Solar-Terrestrial Phys. Due to its relative unreliability, shortwave radio communication has been mostly abandoned by the telecommunications industry, though it remains important for high-latitude communication where satellite-based radio communication is not possible. Specific mechanisms, such as tidal amplification (Goncharenko et al., 2010; Klimenko et al., 2019) and specific ionosphere signatures (Immel et al., 2006) have been identified. 66, 36813691. J. Geophys. (2006). Dordrecht: Springer Netherlands, 303316. doi:10.1029/2000JA000035, Huba, J. D., and Joyce, G. (2014). Solar-Terrestrial Phys. Simulations suggest that variability in thermosphere winds also affects global EB drifts in the inner magnetosphere so as to affect the shape of the plasmasphere. [19] In fact, absorption levels can increase by many tens of dB during intense events, which is enough to absorb most (if not all) transpolar HF radio signal transmissions. Res. Lightning can cause ionospheric perturbations in the D-region in one of two ways. Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Science at the Crossroads of the Earth's Atmosphere. Vitaly Ginzburg has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere. 1, shown in Figure 1A, demonstrates that the effect of the O density is fully consistent with the outflow formulation of Richards and Torr (1985). 2, 301319. J. Geophys. Previously, the H-O+ charge exchange reaction rate was based on data for the reverse reaction (Fehsenfeld and Ferguson, 1972) and the finding that the ratio of the forward to reverse reaction rates is 9/8 (Hanson and Ortenburger, 1961). Earth Space Sci. [8] Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. The thermosphere is the region of the Earth's atmosphere between about 100 km and 500 km above the Earth's surface. Due to the ability of ionized atmospheric gases to refract high frequency (HF, or shortwave) radio waves, the ionosphere can reflect radio waves directed into the sky back toward the Earth. The X-rays penetrate to the D-region, releasing electrons that rapidly increase absorption, causing a high frequency (330MHz) radio blackout that can persist for many hours after strong flares. doi:10.1029/2019GL084327, Cucho-Padin, G., and Waldrop, L. (2018). (2014) study of Figure 2, showed that, when one wind model was exchanged for another, the shape of the model plasmasphere changed. Solar-Terrestrial Phys. Space Phys. J. Geophys. Because the solar cycle so strongly affects thermosphere and exosphere composition, the variation of cold H+ refilling outflows with the solar cycle, specifically with the F10.7 extreme ultraviolet (EUV) index, is quite counter-intuitive. (2016b). NASA's heliophysics researches the ionosphere-thermosphere-mesosphere region where our neutral atmosphere transitions into the ionized plasma of space. J. Geophys. Open Archive. Specifically, the Krall et al. The SAMI2 code, which simulates a single magnetic-longitude plane, runs quickly enough to support parameter studies such as described here. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions). Reduction rules are given in: "URSI Handbook of Ionogram Interpretation and Reduction", edited by William Roy Piggott and Karl Rawer, Elsevier Amsterdam, 1961 (translations into Chinese, French, Japanese and Russian are available). Toggle Persistent anomalies to the idealized model subsection, Toggle Ephemeral ionospheric perturbations subsection, Toggle Indices of the ionosphere subsection, Persistent anomalies to the idealized model, X-rays: sudden ionospheric disturbances (SID), Ionospheres of other planets and natural satellites. FIGURE 1. Res. A Three-Dimensional Dynamic Kinetic Model of the Plasmasphere. doi:10.1029/2020JA028947, PubMed Abstract | CrossRef Full Text | Google Scholar, Hedin, A. E. (1987). 21, 417420. Temporal Variability of Atomic Hydrogen from the Mesopause to the Upper Thermosphere. Space Phys. Res. 37, 1-6. doi:10.1029/2010GL043125, Hanson, W. B., and Ortenburger, I. Res. These particles can hit the Earth within 15 minutes to 2 hours of the solar flare. Ionization is due to soft X-ray (110nm) and far ultraviolet (UV) solar radiation ionization of molecular oxygen (O2). The Earth's magnetic field lines are horizontal at the magnetic equator. Space Phys. J. Geophys. J. Geophys. Res. Four numerical simulations have been performed, at equinox, using a coupled thermosphere-ionosphere model, to illustrate the response of the upper atmosphere to geomagnetic storms. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. In May 2023, Frontiers adopted a new reporting platform to be Counter 5 compliant, in line with industry standards. Specifically, winds effect the degree to which the ionosphere, which is most strongly generated near the sub-solar point, is transported to the mid-to-high latitudes that are the source of the plasmasphere. New observations of thermosphere winds on a global scale are presently coming from the NASA Ionospheric Connection Explorer (ICON) (Immel et al., 2018). doi:10.1007/978-94-007-0326-1_22, Makela, J. J., Baughman, M., Navarro, L. A., Harding, B. J., Englert, C. R., Harlander, J. M., et al. where Space Phys. Whistler Observations of the Interchange of Ionization between the Ionosphere and the Protonosphere. A Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM): Equinox Solar Cycle Minimum Simulations (30500 Km). Geophys. (2015). J. Geophys. Incoherent scatter radars operate above the critical frequencies. This effect is known as the winter anomaly. Electron production is dominated by extreme ultraviolet (UV, 10100nm) radiation ionizing atomic oxygen. doi:10.1029/2003JA010165, Bortnik, J., and Thorne, R. M. (2007). doi:10.1029/94JA02183, Horwitz, J. L., Comfort, R. H., and Chappell, C. R. (1990). An ionosonde sweeps a range of frequencies, usually from 0.1 to 30MHz, transmitting at vertical incidence to the ionosphere. doi:10.1029/JA092iA05p04649, Hedin, A. E. (1991). doi:10.1063/1.1677642, Forbes, J., Zhang, X., and Bruinsma, S. (2014). 154, 132166. J. Geophys. Light ions, H+ and He+, commonly flow upward from the topside ionosphere. Res. However, recent analysis (Stancil et al., 1999) and measurements (Waldrop et al., 2006; Joshi and Waldrop, 2019) suggest that this ratio is somewhat (14%) larger, increasing the coefficient in the reaction rate, and in Eq. The F2 layer persists by day and night and is the main region responsible for the refraction and reflection of radio waves. Note: these results (Krall and Huba, 2019a) use 2.50 instead of 2.85 in Eq. The Naval Research Laboratory (NRL) Sami2 is Another Model of the Ionosphere (SAMI2) and Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere codes have shown that thermosphere composition and winds significantly affect H+ outflows from the topside ionosphere. Unexpected Connections between the Stratosphere and Ionosphere. Geophys. Res. At mid-latitudes, the F2 layer daytime ion production is higher in the summer, as expected, since the Sun shines more directly on the Earth. The Earths space environment covers the region above about 80 km altitude, where electromagnetic effects become significant. Language links are at the top of the page across from the title. J. Atmos. doi:10.1029/JA090iA06p05261, Rishbeth, H. (1998). J. Geophys. The Breathing Plasmasphere: Erosion and Refilling. The Maximum Usable Frequency (MUF) is defined as the upper frequency limit that can be used for transmission between two points at a specified time. Charge Transfer in Collisions of O with H and H with O. Astron. At solar maximum (red curves) the diffusion effect tends to dominate, slowing outflow and refilling. Further, because tides transport O density (Jones et al., 2014), wind variability could be a source of density variability. The Effect of the Thermosphere on Quiet Time Plasmasphere Morphology. It is one of the layers that make up the Earth's atmosphere characterized by X-rays, gamma and ultraviolet rays that cause sodium molecules and atoms to ionize, increasing the temperature.. Due to this peculiarity, the thermosphere includes the ionosphere, where . SAMI3 simulates the interaction between ionosphere and plasmasphere ion populations and the thermosphere (Huba and Liu, 2020) and magnetosphere (Huba et al., 2005; Huba and Sazykin, 2014). The cutoff frequency is the frequency below which a radio wave fails to penetrate a layer of the ionosphere at the incidence angle required for transmission between two specified points by refraction from the layer. Thermosphere dynamics and ionosphere outflows at polar latitudes, a much bigger subject, will not be addressed. J. Geophys. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS-A and -B in 1972 and 1975, all for measuring the ionosphere. Res. doi:10.1002/essoar.10500701.1, Klimenko, M. V., Klimenko, V. V., Bessarab, F. S., Sukhodolov, T. V., Vasilev, P. A., Karpov, I. V., et al. [13] On board radio beacons on this satellite (and its successors) enabled for the first time the measurement of total electron content (TEC) variation along a radio beam from geostationary orbit to an earth receiver. doi:10.1002/2015SW001223, McIlwain, C. E. (1961). 214, 14. Numerical Methods in Modeling the Ionosphere. Their power spectrum contains information not only on the density, but also on the ion and electron temperatures, ion masses and drift velocities. doi:10.1029/2019JA027057, Joshi, P. P., Waldrop, L. S., and Brum, C. G. M. (2018). This implies that day-to-day variability in thermosphere tides, which is known to be present for some tidal components, might be a cause of similar variability in exosphere H densities. 1, and the simulated outflow flux above Z0. (1999). Res. Res. It is calculated as shown below: where N = electron density per m3 and fcritical is in Hz. The first is through VLF (very low frequency) radio waves launched into the magnetosphere. Geophys. Received: 20 May 2021; Accepted: 23 June 2021;Published: 16 July 2021. A comprehensive numerical model, the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X), has been improved, in order to simulate the entire atmosphere and ionosphere, from the Earth's surface to 700 km altitude. The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Their subsequent research has focused on the mechanism by which this process can occur. doi:10.1002/2016JA023247, Lawrence, D. J., Thomsen, M. F., Borovsky, J. E., and McComas, D. J. Coronal mass ejections can also release energetic protons that enhance D-region absorption in the polar regions. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer. J. Atmos. Res. ionosphere and the densities of minor, photo- and electro-chemically produced constituents. J. Chem. Space Phys. Res. 126, e2020JA028727. 126, e2020JA028726. A New Dynamic Fluid-Kinetic Model for Plasma Transport within the Plasmasphere. External Source. In 1924 its existence was detected by Edward V. Appleton and Miles Barnett. Evidence for these effects is reviewed and prospects for forecasting these outflows are explored. In the partially ionized transition region between the atmosphere and space, in the thermosphere, and in the ionosphere, chemical as well as dynamic processes are important, as are the gravitational forces and neutral gas processes. The active, changing layer Sporadic E propagation makes VHF-operating by radio amateurs very exciting when long distance propagation paths that are generally unreachable "open up" to two-way communication. Unsolved Problems in Plasmasphere Refilling. Bishop, J., Harlander, J., Nossal, S., and Roesler, F. L. (2001). As a group, these regions are collectively called the ionosphere. 111, 114. Day-to-day Variability of the Bottomside Ionosphere. doi:10.1002/2015JA021047, Fang, T.-W., Akmaev, R., Fuller-Rowell, T., Wu, F., Maruyama, N., and Millward, G. (2013). Creative Commons Attribution License (CC BY). Space Phys. In 2005, C. Davis and C. Johnson, working at the Rutherford Appleton Laboratory in Oxfordshire, UK, demonstrated that the Es layer was indeed enhanced as a result of lightning activity. Something went wrong. Quantification of the Vertical Transport and Escape of Atomic Hydrogen in the Terrestrial Upper Atmosphere. In the next section, the effect of thermosphere composition, particularly the O density, will be demonstrated using SAMI2. Sami2 Is Another Model of the Ionosphere (Sami2): A New Low-Latitude Ionosphere Model. NRLMSISE-00 Empirical Model of the Atmosphere: Statistical Comparisons and Scientific Issues. Scientists explore the structure of the ionosphere by a wide variety of methods. Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (18611939) and the British physicist Oliver Heaviside (18501925). 5. doi:10.1002/9781118704417.ch5, Huba, J. D., Joyce, G., Sazykin, S., Wolf, R., and Spiro, R. (2005). Sporadic-E events may last for just a few minutes to many hours. Shortwave broadcasting is useful in crossing international boundaries and covering large areas at low cost. ICON is equipped with a Michelson interferometer, built by the NRL, that measures winds and temperatures in the altitude range 90300km (Harding et al., 2021; Makela et al., 2021). This work summarizes the state of the solar wind before and during the geomagnetic storm, the response of the plasmasphere-ionosphere-thermosphere system in the European sector and, for a comparison, the ionosphere-thermosphere response of the American . (2008). 121, 22262248. doi:10.1016/j.jastp.2006.06.019, Nossal, S. M., Mierkiewicz, E. J., and Roesler, F. L. (2012). J. Geophys. J. Geophys. The O density inhibits upward diffusion; this sensitivity to the O density is not explicit in Eq. The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) is a comprehensive, first-principles, three-dimensional, non-linear representation of the coupled thermosphere and ionosphere system that includes a self-consistent solution of the middle and low-latitude dynamo field. The Klobuchar model is currently used to compensate for ionospheric effects in GPS. doi:10.1002/2017JA024998, Qin, J., Waldrop, L., and Makela, J. J. Storm Time Ionosphere and Plasmasphere Structuring: Sami3-RCM Simulation of the 31 March 2001 Geomagnetic Storm. HSS/CIR driven storm effects on the ionosphere-thermosphere system. Recent simulations showing model-data agreement for ionosphere/thermosphere interactions on a global scale (Huba and Liu, 2020) suggest that such modeling might soon reproduce ducts, crenelations, and other elements of observed plasmasphere structure (Horwitz et al., 1990). Author JH was employed by Syntek Technologies. As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out steadily declines as the electrons in the D-region recombine rapidly and propagation gradually returns to pre-flare conditions over minutes to hours depending on the solar flare strength and frequency. J. Geophys. 121, 68896900. Diurnal variability has been quantified (Qian et al., 2018), but does not necessarily imply day-to-day variability. We thank Lara Waldrop of University of Illinois at Urbana-Champaign, Susan M. Nossal of University of Wisconsin-Madison, McArthur Jones Jr of NRL, and Alan G. Burns of NCAR for helpful discussions. 92, 46494662. The anomaly is always present in the northern hemisphere, but is usually absent in the southern hemisphere during periods of low solar activity. FIGURE 2. Suppl. Phys. In addition, winds affect the quiet-time latitudinal extent of the F layer, affecting densities at mid-to-high latitudes that are the source of plasmasphere refilling outflows. This model was developed at the US Air Force Geophysical Research Laboratory circa 1974 by John (Jack) Klobuchar. A., et al. The returning radio waves can reflect off the Earth's surface into the sky again, allowing greater ranges to be achieved with multiple hops. doi:10.1002/2014GL062110, Immel, T. J., England, S. L., Mende, S. B., Heelis, R. A., Englert, C. R., Edelstein, J., et al. However, we can instead obtain a thermosphere specification from a first-principles model, such as the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) (Roble and Ridley, 1994). The skip distances are generally around 1,640km (1,020mi). doi:10.1029/JZ071i005p01421, Drob, D. P., Emmert, J. T., Meriwether, J. W., Makela, J. J., Doornbos, E., Conde, M., et al. Objects in the Solar System that have appreciable atmospheres (i.e., all of the major planets and many of the larger natural satellites) generally produce ionospheres. (The rotation of the plane of polarization directly measures TEC along the path.) (2020). What is the magnitude of day-to-day variability, if any, in the thermosphere O density? Res. The term 'ionosphere', for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series.